In the process of producing oil and/or gas wells, fluids from the surface often need to be injected into the wellbore through a supply conduit. Such fluids include, for example, chemicals to inhibit corrosion of the production tubing string in deleterious subsurface environments and hydrualic fluids to control safety valves.
The need for hydraulic fluids to control subsurface safety valves is especially pertinent to offshore wells. In emergencies brought about by bad weather conditions, for example, a danger may exist that the production string may be severed or severely damaged, resulting in uncontrolled flow of hydrocarbons from the well. To prevent such an occurrence, it is accepted practice to provide safety devices disposed along the tubing string and below the mud line for shutting off the flow of the well.
These safety devices generally comprise one or more valves hydraulically actuatable from the surface and thus in fluid communication with the aforementioned supply conduit. Upon sensing fluid pressure change in the conduit (brought about by a severing of the conduit or effected on the surface at a control panel by wellsite personnel), a closure member in the valve will shut in the well.
Many other instances arise wherein control of downhole apparatus, such as sliding sleeves known in the art, is desirably effected by means of a surface-actuated hydraulic control line extending into the wellbore or borehole. Moreover, several situations occur wherein the pathway of the fluid or pressure routed downhole in the supply conduit must be re-routed to a different location or elevation within the borehole.
For example, in the case of the aforementioned offshore wells, it is preferred practice to provide for redundancy in the form of multiple safety valves at various borehole elevations in the event one safety valve should fail. Thus, a conventional "tubing-retrievable" subsurface safety valve, well known in the art, is typically provided in the production string which is surface-controlled by the supply conduit.
In addition, a second back-up subsurface safety valve at a different borehole elevation may be further provided in series with the production string. This second valve will also desirably be hydraulically controllable from the surface in like manner. Such a valve may take the form of an "insert" safety valve, also conventionally known in the art. The use of such valves is generally described below.
One or more landing nipples are disposed along the tubing string at desired locations. An insert safety valve is then installed or "landed" in each nipple or retrieved therefrom, as desired, by means of an appropriate wire line tool, through-flow line technique, or the like, also well known in the art.
Each insert safety valve will be actuatable hydraulically from the surface by means of a hydraulic supply conduit. In order to selectively actuate each such safety valve, it would thus conventionally be necessary to provide a separate supply conduit aligned adjacent the tubing string and extending to the surface to provide control fluid pressure to each valve.
Thus, in the alternative, it would be highly desirable to have the downhole capacility to re-route from a single supply conduit, control or other fluids or hydraulic actuating pressure to any desired safety valve in the string. This would thereby obviate the need for inherently undesirable multiple supply conduits which, due to multiple fluid connections and the like, compound reliability problems such as leakage.
Finally, with regard to the aforementioned hydraulically sliding sleeves and the like, which may be simultaneously present in the string along with safety valves, it is also desirable to be able to selectively control each such device from one fluid control line traversing the formation.
Accordingly, methods and apparatus were highly sought after for the downhole re-routing of hydraulic actuating control fluids and pressures as well as chemicals or other fluids as desired. Moreover, such methods and apparatus were desired which were reliable and did not interfere with the normal operation and flow of the tubing string.